US20130312440A1

Movatterモバイル変換

Info

Publication number: US20130312440A1
Application number: US13/479,908
Authority: US
Inventors: Ching-Jen Tang; William Dwight Gerstler
Original assignee: General Electric Co
Current assignee: Haier US Appliance Solutions Inc
Priority date: 2012-05-24
Filing date: 2012-05-24
Publication date: 2013-11-28

Abstract

An absorption chiller system is provided. The system includes an evaporator, an absorber, a divider, a recirculating loop, and a primary heater. The evaporator includes a first working fluid inlet and a first working fluid outlet. The absorber includes a second working fluid inlet and a second working fluid outlet. The divider has opposing first and second sides, wherein the first side is in fluid communication with the evaporator and the second side is in fluid communication with the absorber. The recirculating loop connects the first working fluid outlet back to the evaporator, and the primary heater is disposed in thermal communication with the recirculating loop.

Description

BACKGROUND

This invention relates generally to an absorption chiller system. Particularly the invention relates to an absorption chiller system including an external recirculating loop for a working fluid.

Absorption chillers are thermally driven temperature lift devices where heat sources provide the driving thermal energy. Absorption chillers are environmentally friendly and generally use less electrical energy compared to conventional coolers that use electrically driven vapor compressors to provide the primary driving energy. Absorption chillers provide a cooling effect by evaporating a refrigerant in an evaporator. The resultant refrigerant vapor is then combined with an absorbent in an absorber. The absorption chillers may be powered by different means, including natural gas, steam, or waste heat.

Crystallization of the absorbents such as lithium bromide in the absorber is one of the classic technical challenges for commercializing absorption chillers. Membrane-based absorption chillers generally help in reducing the crystallization of the absorbents. Further control of crystallization of absorbents at the absorber, thereby enabling the absorption chillers to operate in a wide temperature range, is an existing need. Embodiments of the present invention relate to the systems and methods that enable further reduction in crystallization of absorbent at the absorber.

BRIEF DESCRIPTION

Briefly, in one embodiment, a system is provided. The system includes an evaporator, an absorber, a divider, a recirculating loop, and a primary heater. The evaporator includes a first working fluid inlet and a first working fluid outlet. The absorber includes a second working fluid inlet and a second working fluid outlet. The divider has opposing first and second sides, wherein the first side is in fluid communication with the evaporator and the second side is in fluid communication with the absorber. The recirculating loop connects the first working fluid outlet back to the evaporator, and the primary heater is disposed in thermal communication with the recirculating loop.

In one embodiment, a system is provided. The system includes an evaporator, an absorber, a divider, a recirculating loop, a primary heater, and a secondary heater. The evaporator includes a first working fluid inlet and a first working fluid outlet. The absorber includes a second working fluid inlet and a second working fluid outlet. The divider can be a hydrophobic porous membrane and has opposing first and second sides, wherein the first side is in fluid communication with the evaporator and the second side is in fluid communication with the absorber. The recirculating loop connects the first working fluid outlet back to the evaporator. The primary heater is disposed in thermal communication with the recirculating loop and the secondary heater is disposed in thermal communication with the evaporator.

In one embodiment, a method is disclosed. The method includes the steps of evaporating at least a part of a first working fluid in an evaporator, passing at least a part of the first working fluid vapor through a divider to an absorber that includes a second working fluid, exiting at least a part of the first working fluid through a first working fluid outlet of the evaporator, heating at least a part of the first working fluid after departing from the first working fluid outlet, and recirculating at least a part of the heated first working fluid back to the evaporator.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an absorption chiller system, according to an embodiment of the invention;

FIG. 2 illustrates arrangement of primary heater according to an embodiment of the invention;

FIG. 3 illustrates an absorption chiller system as per an example according to one embodiment of the invention;

FIG. 4 illustrates arrangement of primary heater according to an embodiment of the invention;

FIG. 5 illustrates a Dühring plot as per an example according to one embodiment of the invention; and

FIG. 6 compares the vapor pressures of a conventional system with an absorption chiller, according to one embodiment of the invention.

DETAILED DESCRIPTION

One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

In the following specification and the claims that follow, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

Referring toFIG. 1, a part of anabsorption chiller system10, configured in accordance with an example embodiment, is shown. Thesystem10 can include anevaporator12 and anabsorber14. Adivider16 may be disposed between theevaporator12 and theabsorber14. In one embodiment, thedivider16 may be a membrane. Thedivider16 has opposing first18 and second20 sides with theevaporator12 being in fluid communication with thefirst side18 and the absorber14 being in fluid communication with thesecond side20. For example, in one embodiment, theevaporator12 can be coupled to thefirst side18 and theabsorber14 can be coupled to thesecond side20.

Theevaporator12 may have a first workingfluid inlet22 and a first workingfluid outlet24. Theevaporator12 may be configured to receive a first working fluid (refrigerant)26 and to produce first workingfluid vapor28. For example, in one embodiment, the first workingfluid26 may be water, and theevaporator12 may receive liquid water (for example, through first working fluid inlet22) and may producewater vapor28. Other candidate first working fluids are discussed below. Liquid first workingfluid26 may circulate through theevaporator12, and the unevaporated portions are emitted from the evaporator, for example, at the first workingfluid outlet24.

Thedivider16 can be disposed between, and in fluid communication with, theevaporator12 and the absorber14. Thefirst side18 of thedivider16 therefore may be contacted by liquid first workingfluid26 and the first workingfluid vapor28, and thesecond side20 may be contacted by the second workingfluid36 and first workingfluid vapor28 that may be disposed in theabsorber14. In some embodiments, virtually all of the volume within theevaporator12 may be occupied by liquid first workingfluid26 and/or all of the volume within theabsorber14 may be occupied by the second workingfluid36. In such cases, first workingfluid vapor28 in theevaporator12 would be found mainly at thepores38 of thedivider16.

Thedivider16 may be configured to allow first workingfluid vapor28 to pass through between the first and

second sides

18,20, and to inhibit movement of liquid first workingfluid26 and the second workingfluid36 through between said first and second sides. For example, thedivider16 may defineholes38 there through. Theholes38 may be sized in accordance with the properties of the first and

second working fluids

26,36 and those of the material making up thedivider16 in order to assure that the interfacial energies of liquid first and second working fluids and the membrane are such that the liquid first and second working fluids are energetically prevented from assuming a configuration necessary to pass through the holes in the membrane.

The second workingfluid36 may be chosen such that, when received at the absorber14 (under appropriate conditions), an equilibrium partial pressure P2 of first workingfluid vapor28 at the second side20 (and possibly throughout the absorber) is less than a partial pressure P1 of first working fluid vapor at the first side18 (and possibly throughout the evaporator12). For example, the first and second working

fluids

26,36 may be chosen such that the second working fluid includes as a component thereof a liquid that has a strong affinity for the first working fluid. In such a case, the equilibrium partial pressure P2 of the first workingfluid vapor28 in the vicinity of the second workingfluid36 will tend to be low relative, for example, to the partial pressure P1 expected in the vicinity of liquid first workingfluid26. Examples of pairs of first and second working

fluids

26,36 that may be utilized in conjunction with embodiments of the above describedsystem10 include, but are not limited to, water and lithium bromide; NH₃and water (or a mixture of water and NH₃); water and LiClO₃; water and CaCl₂, water and ZnCl₂; water and ZnBr; water and H₂SO₄; and SO₂and organic solvents.

The difference in partial pressures P1 and P2 of first workingfluid vapor28 across thedivider16 results in a driving force for diffusion of first working fluid vapor from thefirst side18 to thesecond side20. Once first workingfluid vapor28 reaches thesecond side20, it can be combined in theabsorber14 with the second workingfluid36, with this combination being made more likely by the proper choice of a second working fluid having an affinity for first working fluid. Mass of first workingfluid26 will therefore be transferred from theevaporator12 to theabsorber14 in the form of avapor28.

As mass is transferred from theevaporator12 to theabsorber14, the balance in the evaporator between liquid first workingfluid26 and first workingfluid vapor28 will be disrupted, resulting in reducing the temperature of the first working fluid or absorbing external thermal energy. It is noted that continued evaporation of liquid first workingfluid26 in theevaporator12 does not necessarily require the input of external thermal energy, but instead may proceed simply due to the affinity of the second workingfluid36 for first working fluid. The evaporation will stop when the pressure of the first workingfluid vapor28 balances the saturated pressure of the first workingfluid26.

In the conventional chillers, the total pressure within either the evaporator or the absorber needs to be approximately the same as the respective partial pressure therein of first working fluid vapor. With theevaporator12 and theabsorber14 separated by thedivider16 as discussed above in various embodiments of the invention, it may not be required that the total pressure within either of the evaporator or the absorber is approximately the same as the respective partial pressure therein of first workingfluid vapor28. Rather, theevaporator12 may be configured such that the total pressure therein is greater than the partial pressure P1 of first workingfluid vapor28. In one embodiment, the total pressure at the evaporator is at least twice the partial pressure P1 of first workingfluid vapor28. Further, theabsorber14 may be configured such that the total pressure therein is at least twice the partial pressure P2 of first workingfluid vapor28. As such, embodiments of thesystem10 may have a total size and weight that is significantly reduced with respect to conventional absorption chiller sub-systems.

For the first workingfluid vapor28 to be driven from one side of thedivider16 to the other, particular temperatures and pressures are desired. As mentioned above, the evaporation of liquid first workingfluid26 in theevaporator12, the diffusion of first workingfluid vapor28 from thefirst side18 of thedivider16 to thesecond side20, and the absorption of first working fluid vapor (or other energy-releasing event) in theabsorber14 can proceed spontaneously, acting to transfer thermal energy from the evaporator to the absorber. However, as thermal energy is transferred, the temperature of the liquid first working fluid26 (in the absence of any other energy transfers) may drop, thereby reducing (and eventually eliminating) the tendency for further evaporation. At the same time, the temperature of the second working fluid36 (again, in the absence of any other energy transfers) will rise, thereby decreasing (and eventually eliminating) the tendency of first workingfluid vapor28 therein to be absorbed. It is noted that, in some embodiments, thedivider16 may include a thermally insulating material, thereby preventing the transfer of heat through from theabsorber14 to theevaporator12.

In one embodiment, the primary workingfluid26 exiting from the first workingfluid outlet24 of theevaporator12 may be recirculated to theinlet22 of theevaporator12 through arecirculating loop40. Therecirculating loop40 may recirculate the first working fluid to the evaporator through the first workingfluid inlet22 or through any other point in between the first workingfluid inlet22 and the first workingfluid outlet24 in theevaporator14. For example, therecirculating loop40 may join theevaporator14 at any of the

points

42,44,46 of the evaporator.

Generally, the temperature of the refrigerant in the evaporator decreases from the inlet to outlet. In one embodiment, the temperature of the recirculated liquid refrigerant is lower than the refrigerant temperature at theinlet22 and higher than the refrigerant temperature at theoutlet24. In one embodiment, it is desirable that the recirculated refrigerant meet the refrigerant in the evaporator at a point where temperature of the recirculated refrigerant matches temperature of the refrigerant in the evaporator. As a result, more vapor can be transferred to the absorber in the beginning part of the absorber, leading to increasing the crystallization margin.

In one embodiment, in order to allow the transfer of vapors from theevaporator12 to theabsorber14 to continue, the first workingfluid26 exiting theevaporator12 through therecirculating loop40 is brought into thermal communication with a thermal energy source, such as aprimary heater50. As used herein, “thermal communication” means the thermal energy transfer in between theprimary heater50 and therecirculating loop40. In one embodiment, the thermal energy is transferred from theprimary heater50 to therecirculating loop40. The thermal communication with theprimary heater50 increases the temperature of the recirculated first workingfluid26 entering the evaporator12 (may be through any one or all the

points

22,42,44,46). The temperature increase of the recirculated first workingfluid26 increases the partial pressure P1 of the first working fluid at theevaporator12. The increased partial pressure P1 of the first working fluid atfirst side18 further promotes the first workingfluid vapor28 transferring to theabsorber14 through thedivider16.

In one embodiment, theprimary heater50 is aheat exchanger50 in fluid communication with a heat-source60 as shown inFIG. 2. As used herein, the “fluid communication” means that theprimary heater50 and a heat source are connected through at least one fluid-passing conduit. In one embodiment, theprimary heater50 and therecirculating loop40 are in fluid communication with each other. As used herein, a heat exchanger is a device, wherein thermal energy is transferred from one part to another. In one embodiment, a heat exchanger includes at least two fluid passing conduits, wherein the thermal energy is transferred from one conduit to another. Theheat exchanger50 may be configured to pass the heat from the heat-source60 to therecirculating loop40.

In one embodiment, thesystem10 may further have asecondary heater70 disposed in thermal communication with evaporator as shown inFIG. 3. Similar toprimary heater50, in one embodiment, thesecondary heater70 is aheat exchanger70 in fluid communication with a heat-source80 as shown inFIG. 4. In a further embodiment, thesecondary heater70 is in fluid communication with theevaporator12. In one embodiment, the heat-source60 that is in fluid communication withprimary heater50 and theheat source80 that is in fluid communication with thesecondary heater70 are the same as shown inFIG. 4. In an instance of a same heat-source60/80 supplying thermal energy to theprimary heater50 and thesecondary heater70, the primary50 and the secondary70 heat exchangers may have a parallel fluid communication with the heat-source60/80 as shown inFIG. 4 or may have a series or successive fluid communication with the heat-source60/80 as shown inFIG. 5. Depending on the design and operations requirement of thesystem10, in an instance of successive fluid communication with the primary50 and secondary70 heat exchangers with the heat-source60/80, the thermal communication may happen first with theprimary heat exchanger50 or thesecondary heat exchanger70.

In one embodiment, in order to allow the transfer of thermal energy from theevaporator12 to theabsorber14 to continue, the absorber may be brought into thermal communication with a thermal energy sink (not shown). For example, a fluid stream (e.g., air or water) may be circulated between theabsorber14 and the thermal energy sink. Thesystem10 can therefore be used to extract thermal energy from the heat-

sources

60,80 and to deposit thermal energy at a thermal energy sink.

During operation of thesystem10, a generator (not shown) may receive the relatively diluted second workingfluid36 that is outputted at the second workingfluid outlet34 of theabsorber14. As mentioned above, the second workingfluid36 that is outputted from theabsorber14 has been combined therein with first workingfluid vapor28 passing through thedivider16. The generator may be configured to receive the relatively diluted second workingfluid36 and to produce separate outputs of first workingfluid vapor28 and a relatively concentrated second workingfluid36. For example, thermal energy can be added at the generator to raise the temperature of the relatively diluted second workingfluid36, thereby driving some of the first working fluid dissolved therein out of the solution as first workingfluid vapor28. The remaining second working fluid, now being relatively concentrated second workingfluid36, can be directed back to the second workingfluid inlet32 of theabsorber14.

The first workingfluid vapor28 outputted from the generator may be directed to a condenser (not shown) to condense first workingfluid vapor28 and provide liquid first workingfluid26 to theevaporator12. For example, thermal energy may be removed at the condenser, for example, through the use of a heat exchanger, to cause the first workingfluid vapor28 to condense.

Overall, theevaporator12,absorber14, generator, and condenser may operate to form a continuous cycle in which the second workingfluid36 is combined with first workingfluid26 at the absorber and separated from first working fluid at the generator, and first working fluid is converted from vapor to liquid at the condenser and from liquid to vapor at the evaporator.

As described earlier, the use of amembrane16 between the evaporator12 andabsorber14 may alleviate the need to maintain the total pressure in either of the evaporator or the absorber at a level that is about equal to the partial pressure of water vapor in either one. Specifically, each of theevaporator12 and theabsorber14 may be configured such that a respective total pressure therein is greater than or equal to about atmospheric pressure. This may reduce the size, cost, and/or complexity of theevaporator12 andabsorber14. In other embodiments either theevaporator12 or theabsorber14 may be configured to operate either above or below atmospheric pressure and around ambient temperature.

EXAMPLE

The following example illustrates methods, materials, and results, in accordance with specific embodiments, and as such should not be construed as imposing limitations upon the claims. All components are commercially available, unless otherwise indicated.

In one example embodiment, thesystem10 employs water as a first workingfluid26, and a solution of lithium bromide and water as the second workingfluid36 as shown inFIG. 3. Theabsorber14 may be configured to combinewater vapor28 passing through themembrane16 with the lithium bromide-water solution36 entering at aninlet port32, thereby forming in the absorber a lithium bromide-water solution36 that is relatively diluted with respect to lithium bromide content (the solution previously being relatively concentrated with respect to lithium bromide content prior to being combined with water vapor passing through the membrane16). Lithium bromide tends to have a strong affinity for water, such that the partial pressure of water vapor in the vicinity of lithium bromide tends to be relatively low and the diffusion of water vapor through themembrane16 is facilitated. The dilution of the lithium bromide-water solution helps in reducing the crystallization of the lithium bromide at theabsorber14. Theadditional water vapor28 formed at the evaporator due to the thermal communication with theheat exchangers50/70 further helps in evaporation ofwater26 at the evaporator and further reduces the lithium bromide crystallization at the absorber.

As described earlier, in one embodiment, thedivider16 is a membrane. Themembrane16 can defineholes38 that extend between the evaporator12 and theabsorber14. Themembrane16, or at least the portions through which theholes38 are defined, may be formed of substantially hydrophobic material (e.g., polytetrafluoroethylene, polypropylene, and/or polyvinylidene fluoride). By forming theholes38 with a maximum diameter of about 100-500 nm from a substantially hydrophobic material, the movement ofliquid water26 through themembrane16 is substantially prevented, whilewater vapor28 is permitted to pass through the holes between the evaporator12 andabsorber14. As mentioned earlier, in some embodiments, themembrane16 may be formed of thermally insulating material, with examples being the hydrophobic materials listed above.

The vapor pressure of the first working fluid in a conventional design is lower than that for thesystem10 except for the very end section of the evaporator, described herein as shown inFIG. 6. The higher vapor pressure for the embodiments of the invention results from the higher temperature of the first working fluid for the invention. The increase of the vapor pressure of theexample system10 may result in the size reductions of the absorber and evaporator or the increase of the crystallization margin in the absorber.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

1. A system comprising:

an evaporator comprising a first working fluid inlet and a first working fluid outlet;

an absorber comprising a second working fluid inlet and a second working fluid outlet;

a divider having opposing first and second sides, wherein the first side is in fluid communication with the evaporator and the second side is in fluid communication with the absorber;

a recirculating loop connecting the first working fluid outlet to the evaporator; and

a primary heater disposed in thermal communication with the recirculating loop.

2. The system ofclaim 1, wherein the divider comprises a membrane.

3. The system ofclaim 2, wherein the membrane comprises a substantially hydrophobic material.

4. The system ofclaim 2, wherein the membrane comprises a plurality of holes having an average diameter in a range from about 100 nm to about 500 nm.

5. The system ofclaim 1, wherein the recirculating loop connects the first working fluid outlet to the first working fluid inlet.

6. The system ofclaim 1, wherein the recirculating loop connects the first working fluid outlet to the evaporator at a point downstream of the first working fluid inlet.

7. The system ofclaim 1, further comprising a secondary heater disposed in thermal communication with the evaporator.

8. The system ofclaim 7, wherein the primary heater and the secondary heater are heat exchangers in fluid communication with a heat-source.

9. The system ofclaim 8, wherein the heat exchangers are connected to the heat-source in a parallel fluid communication.

10. The system ofclaim 8, wherein the heat exchangers are connected to the heat-source in successive fluid communication.

11. The system ofclaim 7, wherein the primary heater and the secondary heaters are heat exchangers in fluid communication with different heat-sources.

12. A system, comprising:

a hydrophobic membrane based divider having opposing first and second sides, wherein the first side is in fluid communication with the evaporator and the second side is in fluid communication with the absorber;

a recirculating loop connecting the first working fluid outlet to the evaporator;

a primary heater disposed in thermal communication with the recirculating loop; and

a secondary heater disposed in thermal communication with the evaporator.

13. A method comprising:

evaporating at least a part of a first working fluid in an evaporator;

passing at least a part of the first working fluid vapor through a divider to an absorber comprising a second working fluid;

exiting at least a part of the first working fluid through a first working fluid outlet of the evaporator;

heating at least a part of the first working fluid after departing from the first working fluid outlet; and

recirculating at least a part of the heated first working fluid back to the evaporator.

14. The method ofclaim 13, wherein the heated first working fluid is recirculated to a first working fluid inlet of the evaporator.

15. The method ofclaim 13, wherein the heated first working fluid is recirculated to the evaporator at a point downstream of a first working fluid inlet.

16. The method ofclaim 13, wherein the first working fluid comprises water.

17. The method ofclaim 13, further comprising heating the first working fluid inside the evaporator.

18. The method ofclaim 13, further comprising combining the first working fluid vapor with a second working fluid in the absorber.

19. The method ofclaim 18, further comprising cooling at least a part of the second working fluid in the absorber.

20. The method ofclaim 18, wherein the second working fluid comprises a lithium bromide solution.